1. Field of the Invention
The present invention relates to a vehicle suspension system and more particularly to a rear suspension system in which a toe direction control of the wheels can be accomplished by a unique structure thereof including support members, lateral links and the like.
2. Prior art
A suspension system is employed for a motor vehicle so as to prevent the vibration of the wheels from transmitting to the vehicle body or passengers. For this purpose, in Japanese Patent Publication No. 56-47008 published on Nov. 6, 1981 for opposition, there is disclosed a suspension system in which a suspension support structure is provided with a bush of a unique structure mounted between a vehicle body and a suspension support member for improving a vibration absorbing effect. The bush of the suspension system is adapted to be compressed in the up and down direction so as to absorb a vibration of the wheel wherein the coefficient of elasticity of the bush is changed in accordance with the amount of the deformation thereof.
In a motor vehicle, it has been known to provide a suspension system for controlling a toe direction of a wheel. For instance, Japanese Utility Model Publication No. 59-966 published for opposition on Jan. 12, 1984 and corresponding to U.S. Pat. No. 4,245,853, discloses a rear suspension system for suppressing a toe-out movement of the wheel during a turning operation of the vehicle so as to obtain a driving stability. The suspension system disclosed in the Japanese Utility Model Publication No. 59-966 is provided with a tension rod extending longitudinally and two lateral arms extending transversely, one ends of the rod and arms being connected to a suspension support member and the other ends of the rod and arms being connected to a vehicle body.
The lateral arms are connected to the suspension support member through an elastic bush in such a manner that a toe-in movement of the wheel is produced when a side force acts on the wheel.
Further, in Japanese Utility Model Public Disclosure No. 61-48808 laid open to the public on Apr. 2, 1986, there is disclosed a suspension system in which link members are connected swingably in the up and down direction with opposite ends of a suspension cross member at one ends thereof respectively and the other ends of the link members are connected to the right and left wheels respectively. In the disclosed suspension system, the suspension cross member is connected with a vehicle body through a pair of elastic shock absorbing members having different elasticities which are positioned so as to be spaced from each other in the longitudinal direction of the vehicle. The shock absorbing member of the front side is smaller in rigidity than the rear side shock absorbing member so that a toe-in movement is produced in the wheel when a side force acts on the wheel.
Meanwhile, in some vehicles, specifically so called front heavy vehicle in which an engine is mounted at the front side thereof, as a driving force for the wheels is increased, there is produced an under steer action or a power-under trend to deteriorate steering controllability of the vehicle. Although an adequate power-under trend is preferable in terms of a steering stability, it would be undesirable when the trend is too intensified. This problem will be critical specifically in so called four-wheel drive vehicles in which all four wheels can be driven by the engine.
It should be noted however that the conventional suspension system can not accomplish a proper toe-control in response to the magnitude of the driving force for the wheels.